Two way accumulatorprogrammable valve pump

ABSTRACT

An improved implantable valve accumulator pump for the delivery of medication is disclosed. The implantable pump comprises a pressurized drug reservoir. The medication metering assembly comprises a fixed volume accumulator positioned between a pair of valves. The valves alternately open and close to admit medication from the reservoir into the accumulator and to dispense a precise volume pulse to an outlet catheter. In order to improve the pump&#39;s accuracy and to increase pumping volume while optimizing the pump&#39;s overall size and energy usage a two way diaphragm accumulator is used. The unit can be externally programmed or can be used in a fixed rate configuration that is never programmed but set at the factory or in the current programmable configuration.

BACKGROUND OF THE INVENTION

This invention is a direct improvement over the technology of U.S. Pat.Nos. 4,838,887 and 5,049,141, the disclosures of which are herebyincorporated by reference. U.S. Pat. Nos. '887 and '141 describe aprogrammable valve pump overcoming many of the problems of the prior artemploying an accumulator with a diaphragm that deflects in one directionwhen filling with medication and returning to a non-deflected state whenemptying the accumulator. This is demonstrated in FIG. 2A of each ofthese patents. In each case, initial “pumping” is provided by thereservoir which is used to fill the accumulator to its fixed volume. Apressure which is intermediate between the reservoir and the outlet ismaintained behind the accumulator so that it fills and emptiescompletely and rapidly. The accumulator is alternately filled andemptied by the alternate switching of the valves. The rate of switchinggoverns the rate of pumping and thus the delivery rate.

Switching is accomplished by onboard electronics powered by an internalbattery. Once the battery is depleted, or if the battery is rechargeableand it cannot be recharged to an operational level, such devices need tobe explanted and replaced with a new device. Extending the life of thepump through energy efficiency is critical in the design of suchdevices. Energy efficiency can be achieved by increasing the fixedvolume pumped. Increasing the volume pumped can be achieved byincreasing the size of the accumulator in diameter and/or height.However, increased accumulator size can create performance degradationof the existing designs. For example, a higher accumulator requires theaccumulator diaphragm to deflect further. This increase in deflectioncreates a corresponding increase in diaphragm spring force. This in turnwould have a cascading effect on design including the need to increasethe intermediate accumulator and reservoir pressures and to increase therobustness of the pumps design and materials due to the increasedpressure. These changes would adversely affect the size and weight ofthe implant, which by design, should be as small and light aspracticable and would also adversely affect manufacturing costs andefficiencies. They would also adversely affect the filling pressure ofthe pump, would require the diaphragm to be prohibitively thin, makingit hard to manufacture and to meet the life expectancy requirement forsuch a device. In addition, a one-way accumulator limits the maximumpulse size of drug delivery.

An object of this invention is to effect energy efficiency, increasefixed volume pumping and pump performance through a new accumulatordesign while minimizing the aforesaid adverse effects. The new designemploys a “Two Way Diaphragm” that deflects in two directions.

SUMMARY OF THE INVENTION

The problems of the prior art have been overcome by the presentinvention, which provides an infusion apparatus comprising a meteringassembly that includes a valve accumulator pump, the infusion apparatusbeing implantable into a living body. More specifically, the inventionrelates to an infusion apparatus and to a metering assembly including avalve accumulator device for such apparatus that delivers preciseamounts of medication or other fluid at programmed rates. The valveaccumulator pump comprises two valves in fluid communication with afixed volume accumulator. The valves alternately open and close to admitmedication from an infusate reservoir into the accumulator and todispense a precise volume pulse to an outlet catheter or the like. Inorder to improve the accuracy of the pump and to increase pumping volumewhile optimizing the overall size and energy usage of the pump, atwo-way diaphragm accumulator is used.

In certain embodiments, the accumulator includes a chamber housing adiaphragm. The diaphragm provides a barrier between a gas portion of thechamber, and a liquid (infusate) portion of the chamber. When thechamber is devoid of liquid (e.g., the infusate has been discharged),the diaphragm is in a resting position. Upon opening the inlet valve,infusate under pressure enters the fluid portion of the chamber andurges the diaphragm against the bias of the gas in a first (e.g.,upward) direction to fill the chamber with infusate. The inlet valve isthen closed, and upon opening the outlet valve, the gas urges thediaphragm in a second (e.g., downward) direction, forcing the infusateout of the chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an infusion device in accordance withcertain embodiments of the present invention;

FIG. 2 is a schematic diagram of an accumulator having a two waydiaphragm in accordance with certain embodiments of the presentinvention;

FIG. 3 is a top view of a spacer plate in accordance with certainembodiments of the present invention;

FIG. 4 is a cross-sectional view of an accumulator in accordance withcertain embodiments of the present invention; and

FIG. 5 is an exploded perspective view of an accumulator in accordancewith certain embodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

As seen in FIG. 1, the infusion apparatus of the present inventionincludes a metering assembly having a programmable valve accumulatorpump 30, an infusate reservoir 10 that can be conventional andwell-known in the art, and an external programmer 34. Those skilled inthe art will appreciate that an external programmer is not necessary;for example, the device could be used in a fixed rate configuration thatis never programmed but is preset. The reservoir 10 is a sealed housing14 that contains bellows 16 that includes an internal volume thatcontains the medicament or other fluid to be infused. The reservoir ispreferably rechargeable. External of the bellow is a chamber 20 thatcontains a fluid, such as a two-phase fluid having a significant vaporpressure at normal body pressure so that it compresses the bellows andcauses the fluid in the bellows to exit the outlet of the housing 14.The outlet communicates with the metering assembly, such as via abacterial filter 24, the metering assembly generally comprising anaccumulator 30 and an inlet valve 26 and an outlet valve 28 in fluidisolation from the inlet valve. Preferably the metering assembly iselectronically controlled in accordance with convention.

Turning now to FIGS. 4 and 5, accumulator 30 is shown. The accumulator30 includes a housing 50, that together with cap 51 defines a sealed gaschamber 52. The cap 51 is attached to the housing 50 by any suitablemeans, such as laser welding. A suitable gas is sealed, under positivepressure, in the gas chamber 52. The gas chamber 52 is in fluidcommunication with diaphragm chamber 57 via a port 55 in the housing 50.The bottom surface of the housing 50 is configured and positioned toserve as a mechanical stop for the diaphragm 50 when the diaphragm 50 isin the up (fill) position.

Affixed to the housing 50 is a faceplate 56. Preferably the edges of thediaphragm 40 are sandwiched between the housing 50 and faceplate 57 asshown, and the assembly is sealed, such as by laser welding. The volumebetween the housing 50 and faceplate 57, containing the diaphragm 40,defines the diaphragm chamber 57. The diaphragm 40 thus provides abarrier, separating the gas side (e.g., above the diaphragm) from thefluid side (e.g., below the diaphragm) in the accumulator 30. Faceplate56 also includes a fluid inlet port 58 that provides fluid communicationbetween inlet valve 26 and the diaphragm chamber 57, and fluid outletport 59 that provides fluid communication between outlet valve 28 andthe diaphragm chamber 57.

Turning now to FIG. 2, the operation of the accumulator assembly isshown schematically. A normally closed inlet valve 26 is in fluidcommunication with the inlet port 58 of the accumulator 30 (and theoutlet of the reservoir 10 via line 22). A normally closed outlet valve28 is in fluid communication with the outlet port 59 of the accumulator30. Miniature solenoid valves are suitable. Preferably the valves 26, 28are controlled electronically, such as through a module programmed by anexternal programmer 34 (FIG. 1). The outlet of the accumulator 30communicates with a catheter or the like via line 36 that delivers theinfusate to the delivery site in the patient in a conventional manner.

The diaphragm 40, as illustrated in FIGS. 2 and 4, is a circular disk ofa thin metal sheet. Preferably titanium may be used, although othermaterials also may be suitable as determined by those skilled in theart. The disk is selected to have a diameter and thickness of low springrate over the desired range of deflection. Thus, the diaphragm acts as acompliant, flexible wall which separates fluid from the environmentbehind it. The upward and downward motions of the diaphragm 40 arelimited by the bottom surface of the housing 50, and the top surface ofthe faceplate 56, each of which serves as a mechanical stop for thediaphragm, depending on whether the diaphragm chamber 57 is filled withinfusate or is empty of infusate. Thus, these surfaces are provided witha shallow concave profile manufactured into its diaphragm contactsurface. This surface acts as a contour stop for the diaphragm.Dimensions of the contour are chosen to match the general profile of thediaphragm when it is deflected or biased by a predetermined fixedvolume. This predetermined fixed volume is the volume desired to bemetered from the accumulator (e.g., 2 μl).

Deflection of the diaphragm 40 occurs in both the upward and downwarddirection. The fixed volume pumped is essentially twice that pumped by adiaphragm of the same size that is only deflected in one direction inthe same accumulator package configuration. Thus, the Two Way Diaphragmpermits the optimization of accumulator size and energy utilization toincrease fixed volume pumping and to conserve battery energy. The firststep in the FIG. 2 pumping cycle shows the accumulator 30 in a statewhere both the inlet valve 26 and the outlet valve 28 are closed, andthe diaphragm chamber 57 of the accumulator is empty (i.e., devoid ofinfusate fluid). In this condition, preferably the diaphragm 40 isfirmly held against the spacer 70 by the gas and is substantially flat;it is not being urged or deflected in either an upward or downwarddirection (it is noted that the accumulator pressure is generally lessthan the reservoir pressure and diaphragm spring force and greater thanthe catheter outlet pressure). The second step in the cycle shows theaccumulator 30 after the inlet valve 26 has been opened (maintaining theoutlet valve 28 closed). The infusate fluid overcomes the bias of thepressurized gas against the diaphragm 40, and deflects the diaphragm 40upward, thereby filling the diaphragm chamber 57 with fluid from thereservoir 10. The third step in the cycle is the closing of the inletvalve 26 once the diaphragm chamber 57 has been filled to its fixed ordesired volume. The fourth step in the cycle is the opening of theoutlet valve 28 (while maintaining the inlet valve 26 in the closedposition) to empty the diaphragm chamber 57 through the catheter 36,wherein the diaphragm 40 deflects downward as a result of the bias fromthe gas pressure in the gas chamber 52 and in the gas side of thediaphragm chamber 57. Accordingly, the diaphragm 40 deflects in a firstdirection during the filling operation of the accumulator 30, asinfusate fluid under pressure forces the diaphragm upwards against themechanical stop of the bottom surface of the housing 50, overcoming thepressure exerted by the gas in the accumulator. The diaphragm alsodeflects in a second direction during the emptying of the accumulator30, past its flat, resting point position, as the pressurized gas in theaccumulator forces the diaphragm downward against the mechanical stop ofthe top surface of the faceplate 56. The two-way deflection allows twicethe volume to be delivered during a single pumping cycle compared toconventional designs, using the substantially same amount of energy.Preferably the first and second directions of deflection of thediaphragm are opposite directions. The accumulator 30 thus stores anddischarges predetermined volume spikes of infusate at a frequencydefined by the cycling rate of the inlet and outlet valves.

Since the metering assembly controls the flow of fluid from thereservoir and does not rely on constant pressure to initiate flow,although a two-phase liquid can be used in the reservoir, a one-phasegas is suitable as well. Suitable gasses include inert gases such asargon, helium and nitrogen, mixtures thereof, and air.

FIGS. 5A and 5B of the '887 patent illustrate the details of the spacerplate utilized between the medication accumulation chamber and theaccumulator valves. As disclosed in the '887 patent, the continuouscontoured surface desirable to use on the gas-filled side of thediaphragm is undesirable on the fluid side. Intimate contact of tworelatively flat surfaces with a liquid interface will create flowrestrictions when the accumulator is emptied as the plates move towardeach other and during filling when the plates move away from each other.This adverse effect was designed to be overcome by the addition of acheckerboard groove pattern as illustrated in FIG. 5B of the '887patent. Additionally, a circumferential groove was incorporated in thedesign to establish fluid communication between the inlet and the outletvalves. Objects of the design were to: permit complete free flow offluid underneath the flattened diaphragm; assist in washing of areaswhich might otherwise remain stagnant, and; maintain the accumulatordead volume at a minimum level.

U.S. Pat. No. 5,049,141 introduced an improved spacer plate design asillustrated in FIGS. 5A and 5B of that patent, the purpose of which wasto reduce the diaphragm contact area with the plate. It was found thatthe prior art's use of a checkerboard groove provided too much surfacecontact area and therefore large molecule drugs could be crushed at theplate and diaphragm contact points resulting in the creation of drugresidue. The prior art checkerboard design also created areas where thedrug could stagnate and particles and air bubbles could be trapped. The'141 patent introduced an improved spacer plate design utilizingconcentric circumferential grooves to establish fluid communicationbetween the inlet and outlet valves and for fluid communication with thetrough and a design that would reduce the diaphragm and plate contactarea.

The spacer 70 in accordance with certain embodiments of the presentinvention improves upon the prior art with a design that maximizes thewash out of fluid and minimizes dead volume. Channels in the spacer aredesigned to create a flow path that allows the fluid to exit theaccumulator quickly (e.g., the channel flow restriction is kept largeenough to allow the accumulator to empty in a short period of time). Itwas found that the multiple annular grooves of the prior art providedmultiple sites for stagnant fluid and air encapsulation resulting indead volume and a degradation of pumping accuracy. As seen in FIGS. 3and 5, the spacer 70 of the present invention includes an annular groove54 intersected by (and thereby in fluid communication with) a trough 53connecting the inlet and outlet valves wherein the volume of the spacecreated by the annular and trough grooves permits the dead volume in thegrooves and outlets to be equal to or less than about 5% of the totalvolume discharged by the accumulator. Preferably only a single annulargroove 54 is provided, and it is interior to the inlet and outletapertures respectively communicating with the inlet and outlet valves,such that the diameter of the annular groove 54 is smaller than thelength of the trough 53. The groove 54 thus provides an annular flowpath, and the trough 53 provides a lateral flow path between the inletand outlet of the accumulator. Fluid in the groove 54 thus communicateswith the inlet and outlet of the accumulator only through communicationwith the trough 53. The remaining peripheral surface of the space plate50 is preferably flat. The new design flow path configuration andplacement also allows for the fluid to flow out of the accumulatorwithout adversely affecting the empty time.

1. Implantable infusion apparatus, comprising: an infusate reservoir; ametering assembly comprising an accumulator having an inlet and anoutlet; an inlet valve in communication with said reservoir and withsaid accumulator inlet, and an outlet valve in communication with saidaccumulator outlet; a diaphragm disposed in said accumulator such thatsaid diaphragm has a resting state position, and deflects in a firstdirection in response to the opening of said inlet valve while saidoutlet valve is closed to cause infusate to flow into said accumulatorfrom said reservoir, and deflects in a second direction in response tothe opening of said outlet valve while said inlet valve is closed tocause said infusate to flow out of said accumulator outlet, wherein saidfirst and second directions are different from said resting stateposition.
 2. The infusion apparatus of claim 1, wherein said accumulatorfurther comprises a spacer, said spacer having an annular groove and atrough in fluid communication with said annular groove and with saidinlet and outlet of said accumulator, the diameter of said annulargroove being smaller than the length of said trough, said annular grooveand trough defining a fluid flow path.
 3. The infusion apparatus ofclaim 1, wherein said reservoir contains a single phase gas.
 4. Theinfusion apparatus of claim 1, wherein said infusate flows out of saidaccumulator in a series of predetermined volume spikes, the frequency ofsaid spikes being determined by the cycling rate of said first andsecond valves.
 5. An accumulator for an implantable infusion apparatusfor delivering infusate, comprising: a diaphragm chamber having an inletand an outlet, and a diaphragm disposed in said diaphragm chamber, saiddiaphragm having a resting state position in said chamber; and first andsecond valves, each communicating with a respective one of said inletand outlet and cooperatively biasing said diaphragm in a first directionwhen one first valve is open and said second valve is closed, and in asecond direction when said first valve is closed and said second valveis open, wherein said first and second directions are different fromsaid resting state position.
 6. The accumulator of claim 5, furthercomprises a spacer, said spacer having an annular groove and a trough influid communication with said annular groove and with said inlet andoutlet of said accumulator, the diameter of said annular groove beingsmaller than the length of said trough, said annular groove and troughdefining a fluid flow path.
 7. The accumulator of claim 6, wherein thevolume of said fluid flow path is equal to or less than about 5% of thetotal volume of infusate discharged by said accumulator.
 8. Theaccumulator of claim 5, wherein said infusate flows out of saidaccumulator in a series of predetermined volume spikes, the frequency ofsaid spikes being determined by the cycling rate of said first andsecond valves.
 9. The accumulator of claim 5, further comprising a gaschamber containing a pressurized gas, said gas chamber being in fluidcommunication with said diaphragm chamber, wherein said diaphragmprovides a barrier between said pressurized gas and any infusate in saiddiaphragm chamber.
 10. The accumulator of. claim 9, wherein saidpressurized gas biases said diaphragm in said second direction.
 11. Thedevice of claim 10, wherein said bias of said diaphragm by saidpressurized gas is overcome when said first valve is open and saidsecond valve is closed.
 12. An implantable infusion apparatuscomprising: a housing containing an infusate reservoir, a meteringassembly receiving infusate from said reservoir, said metering assemblycomprising a pair of normally closed valves and an accumulatorpositioned in fluid communication with each of said valves, saidaccumulator comprising a chamber containing a diaphragm separating saidchamber into a gas portion and a liquid portion and having a restingposition, and an outlet in fluid communication with said meteringassembly to dispense infusate to a site in a living body, wherein when afirst of said valves is open, infusate flows from said reservoir intosaid accumulator and deflects said diaphragm in a first direction, andwhen the other valve is open and the first closes, said diaphragmdeflects in a second direction, causing said infusate to flow from saidaccumulator into said outlets wherein said first and second directionsare different from said resting position.
 13. The infusion apparatus ofclaim 12, wherein said accumulator further comprises a spacer, saidspacer having an annular groove and a trough in fluid communication withsaid annular groove and with said inlet and outlet of said accumulator,the diameter of said annular groove being smaller than the length ofsaid trough, said annular groove and trough defining a fluid flow path.14. The infusion apparatus of claim 12, wherein said infusate flows outof said accumulator in a series of predetermined volume spikes, thefrequency of said spikes being determined by the cycling rate of saidfirst an second valves.
 15. The infusion apparatus of claim 12, whereinsaid first and second directions are opposite directions.
 16. Theinfusion apparatus of claim 2, wherein said annular groove is the onlyannular groove in said spacer.
 17. The accumulator of claim 6, whereinsaid annular groove is the only annular groove in said spacer.
 18. Theinfusion apparatus of claim 13, wherein said annular groove is the onlyannular groove in said spacer.
 19. The implantable infusion apparatus ofclaim 1, wherein as said diaphragm deflects from said first direction tosaid second direction, it passes through said resting state position.20. The accumulator of claim 5, wherein as said diaphragm deflects fromsaid first direction to said second direction, it passes through saidresting state position.
 21. The infusion apparatus of claim 12, whereinas said diaphragm deflects from said first direction to said seconddirection, it passes through said resting position. 10-14